The present invention relates to a fuel injection valve which injects fuel into an internal combustion engine; and, more particularly, the invention relates to an improved fuel injection valve which provides an excellent fuel spray with regard to both the ignition property and the combustion property thereof.
As an alternative to an in-intake manifold fuel injection device, which injects fuel into an intake manifold of an internal combustion engine, an in-cylinder fuel injection device is known which injects fuel directly into a combustion chamber.
JP-A-6-146886(1994), for example, discloses such an in-cylinder type of gasoline injection engine. In this type of engine, by giving consideration to the position of the fuel injection valve and providing for formation of an intake flow of fuel having a vertical swirl (tumble flow) in the combustion chamber through an intake port extending upward from an intake opening, combustion can be performed stably with a leaner fuel mixture than that at the stoichiometric air fuel ratio, with the result that the fuel economy is improved.
However, the technology used in the above-described engine did not necessarily take into account fully the spray shape or the spray structure necessary to improve both the ignition property (firing property) and the combustion property (reduction of unburnt gas exhaust amount), as will be explained hereinbelow.
In order to optimize the spray injected from a fuel injection valve, it is necessary to take into account the following characteristics. First, there is the spray shape, which is influenced by the spreading angle of the spray and the distance the spray reaches. A second characteristic is the spray particle diameter, in that it is necessary to uniformalize the particle diameter distribution while reducing the number of particles having large diameters as much as possible. A third characteristic is the spray structure, which is required to optimize the space distribution of the sprayed fuel particles in the combustion chamber.
As a result of experimental analysis and study with regard to how these spray characteristics affect the combustion characteristics of an internal combustion engine, the following points need to be considered. In order to improve the ignition property, it is effective to increase the fuel particle distribution around an ignition unit and to enhance the distribution of the air fuel mixture of combustible density. On the other hand, if the fuel particle distribution in the direction of piston movement is reduced, unburnt gas components (HC, CO) in the fuel tend to decrease, so that the combustion property is improved. Further, in order to obtain a combustion stability over a broad range from a low engine rpm to a high engine rpm, it is preferable that the spray shape does not vary with a variation of pressure in the cylinder. This is because, since the geometric positional relationship between a fuel injector and an ignition unit is fixed, in order to always supply a fuel spray of a proper density to the ignition unit, it is important to keep the fuel spray expansion constant. In other words, a fuel spray injected by a conventional fuel injector tends to spread when pressure in a cylinder is low and tends to collapse, when the pressure in the cylinder is high. Therefore, if the arrangement of the fuel injector and the ignition unit is determined with reference to a comparatively high pressure condition of the cylinder, the fuel tends to deposit on an upper and side cylinder face in the cylinder or on the piston head, when the pressure in the cylinder lowers; on the other hand, if a comparatively low pressure condition in the cylinder is selected as a reference, it tends to be difficult for a fuel spray suitable for combustion to reach the ignition unit when pressure in the cylinder rises.